NEW YORK, Dec 19 (Reuters) - Global stock markets added to gains after Federal Reserve Chair Janet Yellen sounded an optimistic tone about the U.S. labor market on Monday, weighing on safe-haven assets like the Japanese yen and U.S. Treasuries that had risen after the shooting death of Russia's ambassador to Turkey.

U.S. stocks initially slipped after the release of Yellen's prepared speech to graduates of the University of Baltimore, but then added to earlier gains.

Wall Street hit record highs last week as investors piled on bets that the anticipated fiscal boost from the incoming administration of U.S. President-elect Donald Trump would support riskier assets.

That trend continued Monday with U.S. equities driven higher by Yellen's rosy outlook and a rise in technology and telecom stocks in a low-volume environment analysts said was typical of the last full trading week of the year.

"Traditionally, as you head into the week before Christmas, you see volumes slow down and a somewhat trendless market as people begin to position their portfolios for next year," said Matt Jones, U.S. head of equity strategy at J.P. Morgan Private Bank in New York.

The Dow Jones industrial average rose 58.81 points, or 0.3 percent, to 19,902.22, the S&P 500 gained 6.61 points, or 0.29 percent, to 2,264.68 and the Nasdaq Composite added 28.68 points, or 0.53 percent, to 5,465.84.

The dollar edged back into positive territory after the release of Yellen's remarks, eyeing a 14-year high against a basket of currencies touched last week.

The Turkish lira and Russian rouble fell to session lows against the greenback on news the Russian ambassador to Turkey was killed in a gun attack at an art gallery in the Turkish capital of Ankara.

The lira was last down about 0.6 percent at 3.525 per dollar while the rouble hit a session low of 62.045 per dollar before retracing to 61.854, according to Reuters data.

The safe-haven Japanese yen added to gains after the report of the ambassador being shot, rising more than 1 percent against the dollar. However, it retraced much of those gains after Yellen's remarks.

"It seems like she is acknowledging the continued improvement in the jobs market. That's pretty consistent with what she and other policymakers have been saying," said Eric Viloria, currency strategist at Wells Fargo Securities in New York.

U.S. Treasury prices pared gains after surging higher following the news from Turkey.

The yield on 10-year U.S. Treasuries, which moves inversely to the note's price, was last 2.55 percent, pushing up from the day's lows.